ci(downgrade): use strict allow-reresolve: false

Flip the Downgrade.yml caller from allow-reresolve: true to the strict
SciML default (false). With false, julia-downgrade-compat resolves each
workspace submodule's [deps] to their floors with transitive deps at
LATEST, and Pkg.test must instantiate that exact set with NO
reconciliation -- the rigorous downgrade that forces the declared [deps]
floors to be genuinely compatible with the latest transitive ecosystem.

Verified locally on Julia 1.10 (deps-mode, Pkg.test(allow_reresolve=false))
per matrix submodule -- ALL PASS at the existing floors, no floor raises
needed beyond those already in this PR:
- DiscreteMeasures.jl: 45/45 (DiscreteMeasure 8, ProductDiscreteMeasure 15,
  Expectation 3, Measure Restrictions 19)
- CanonicalMoments.jl: Orthogonal Polynomial Roots 11/11, Moment Sequence 260/260
- OUQBase.jl: FloodProblem OptimizationBBO solve pipeline completes
  (best candidate [0.344441, 0.831005], fitness 0.1927), tests passed

Co-Authored-By: Chris Rackauckas <accounts@chrisrackauckas.com>
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: ChrisRackauckas

.github/workflows/Downgrade.yml

@@ -28,7 +28,7 @@ jobs:
           - OUQBase.jl
     uses: "SciML/.github/.github/workflows/downgrade.yml@v1"
     with:
-      allow-reresolve: true
+      allow-reresolve: false
       julia-version: "1.10"
       project: "${{ matrix.project }}"
       projects: "${{ matrix.project }}"